An Adaptive Synchronous Driving Phase Control Method of GaN-Based Full-Bridge 6.78-MHz WPTS

The GaN-based active rectifiers have the potential to improve the efficiency of the several megahertz wireless power transfer system (WPTS). The full-bridge active rectifier can eliminate extra dc–dc converters for output regulation with less voltage stress than resonant rectifiers, such as Class E, Φ rectifiers. However, the lack of the synchronous phase control method is the core challenge for full-bridge active rectifier in 6.78-MHz WPTSs. Meanwhile, the increasing switching losses and reverse conduction losses of the gallium nitride high electron mobility transistors are the main constraints on the efficiency of the system. This article proposes an adaptive synchronous driving phase control (ASDPC) method of the GaN-based full-bridge rectifiers in 6.78-MHz WPTS. With the proposed method, the full-bridge rectifier can obtain the maximum output power in the critical zero voltage switching operation over a wide load range. A 50-W 6.78-MHz WPTS is built to verify the effectiveness and stability of the proposed ASDPC method. The dc–dc efficiency is improved in the wide load range of 8–50 Ω (11.8–54.57 W) and reaches 87.18% at P_o = 44.9 W. Compared to the system without ASDPC, the efficiency can be improved by 5.2% at light load and 3.1% at heavy load.